Control circuit for pulse generator



Jan. 14, 1958 c. W EILL ETAL CONTROL CIRCUIT FOR PULSE GENERATOR 2Shee'ts-Sheet 1 Filed June 14, 1954 jib FIG-I3.

z za 24 Pb Inventors C. WEILL' C. HANNIGSBERG H-BH LAAR W47- z/fifi;Attorney Jan. 14; 1958 'c. WEILL r AL CONTROL CIRCUIT FOR PULSEGENERATOR Fiied June 14, 1954 2 Sheets-Sheet 2 wskbwnwk Q9 U i s,

CONTROL CIRCUIT FOR PULSE GENERATOR Camille Weill and ClaudeHannigsberg, Paris, France,

and Hans Adelaar, Antwerp, Belgium, assignors to International StandardElectric Corporation, New York, N. Y., a corporation of DelawareApplication June 14, 1954, Serial No. 436,620

Claims priority, application Netherlands June 17, 1953 6 Claims. (Cl.250-27) S e Pat 9 is to be tolerated since a failure in one circuit willnot I lead to an interruption of the pulse supply if both identicalhalves of the generators are normally supplying the load with half thenecessary power. It is only when there is a fault in one half of theapparatus that this one half will be switched off from the common load,the other half supplying full power during that period in which thefaulty half is being repaired or replaced by a spare circuit.

The essential part of each half of the generator equipment is a masteroscillator which produces pulses of period T which in turn will be usedto produce a variety of auxiliary pulses. It is imperative therefore,that a fault in the circuit of one master oscillator should beimmediately detected so that the circuit can be disconnected from thecommon load before the fault can cause any undesired influence on theshape of the pulses which continue to be supplied by the other masteroscillator circuit. A way to detect a fault is to continuously comparethe pulses issued by both master oscillators with one another and tocause a control circuit to react upon, there being a dissimilaritybetween the pulses compared.

A control circuit of this type, which is essentially a potentialcomparator, has been disclosed in the Belgian Patent No. 504,605 and isa device with three stable electrical conditions. One stable conditioncorresponds to a normal state of afiairs in which identical pulses areissued by both oscillators. The second stable condtion corresponds to apulse being issued by the first oscillator and none being simultaneouslyissued by the second oscillator, while the third stable conditioncorresponds to the opposite situation. Incidentally, such a comparatorwhich stays in its normal condition when the outputs of the twooscillators are similar, will remain in that condition if bothoscillators should fail exactly at the same time since then, theconditions at their outputs will still correspond. However, such alikelihood is so remote that the arrangement can be considered as quitesatisfactory. lf both oscillators should fail simultaneously, all thechances are that this is due to the failure of a common supply which canbe detected by other control means, and not due to simultaneousindividual and independent failures in each oscillator circuit.

Such a comparator has, however, one drawback which is the following:

If, due to some fault in one oscillator circuit, the pulses deliveredfrom that oscillator become longer than the pulses delivered by thesecond oscillator, the comparator can be made to move to one of its offnormal conditions, indicating that the first oscillator is faulty andcausing an alarm to be raised as well as the disconnection of the faultyoscillator from the common load. However, if

a fault occurs in the second-oscillator circ'uit'and such that thelength of the pulses issued by that oscillator is reduced, then thecomparator will react in exactly the same way as before, as it cannotdistinguish between the fact that one pulse is longer than the other andthe fact that the other pulse is shorter than the former. This wouldresult in the first generator being put out of action although it is thesecond which has developed the fault.

An object of the invention is to use a pulse comparator with two inletsand with two of]? normal conditions, one corresponding to a pulse at thefirst inlet with none at the second and the second off normal conditioncorresponding to a pulse at the second inlet and none at the first asvalve control means for two identical pulse generators in such a waythat variations in the length of the pulses delivered by one oscillatorin one sense or the other, including the disappearance of said pulses,always result in the comparator being thrown into one particular oifnormal condition corresponding exclusively with a fault in thatoscillator which delivers pulses of abnormal length.

Another object of the invention resides in the provision of meanswhereby bidirectional variations in the length of a pulse result inunidirectional variations in the length of auxiliary pulses used forcontrol purposes.

In relation to a control circuit for pulse generator, the lattercomprising two identical pulse oscillators with mutual synchronizationbetween corresponding pulse edges and the former a pulse comparator ableto be thrown into a first or a second off normal stable condition upon apulse at one of its two inlets appearing without one at the other orvice versa, a characteristic feature of the invention resides in thatcorresponding pulse edges derived from the first and the secondoscillators are respectively used to trigger a first and a second twocondition device, one of which condition is stable, from the stable tothe unstable condition, the outputs from said devices being respectivelycoupled to the inlets of said comparator, the natural period of saiddevices being smaller than T the period of the pulses from saidoscillators.

In relation to a similar arrangement, another characteristic feature ofthe invention resides in that corresponding pulse edges derived from thefirst and the second oscillators are used to trigger a first and asecond twooutput condition device from a first condition to a secondrespectively, while the other corresponding pulse edges are used torespectively trigger said second and first devices from said second tosaid first condition, the outputs from said devices being respectivelycoupled to'the inlets of said comparator.

The above mentioned and other objects and features of the invention willbecome more apparent and the invention itself will be best understool byreferring to the following description of an embodiment taken inconjunction with the accompanying drawings which represent:

Fig. 1, pulse wave forms useful to explain the principle of theinvention;

Fig. 2, a preferred embodiment of the invention shown in block schematicform;

Fig. 3, pulse wave forms useful to explain the working of thearrangements shown in Fig. 2;

Fig. 4, a block schematic to explain how the arrangement of Fig. 2 canbe integrated in a pulse distributor scheme.

Referring to Fig. 1, which is a preliminary figure necessary for theunderstanding of the invention described in conjunction with Figs. 2 and3, the pulse wave forms delivered by two identical pulse oscillators(not shown) are represented as Pa and Pa respectively. The pulses areshown as positive pulses of duration t recurring with a period T.Normally, the two pulse waves are coinci- 4 gillators are tnutuall syg he j ssued and the comparator will react in the right manmdigated by thelink 1 between ner. the leading edges of the P211 and Pa pulses. Links 2Such an arrangement is satisfactory provided that once and} nespe, ivelylgetvveen the trailing edge of the Ha a pulse such as Pa starts toreduce its pulse length, this p lse a acting edge of the positiveiPb-pulseand 5 soon leads to the complete disappearance of the pulse.

If the pulse length is reduced"to half way for example,

a 1 bif iPam 2211 53199 tti and "remainsat' that length, the comparatorwould "not fies-Eda? i "the t ye Pb21..1 .u a ar used wi a tha tls r. reLobster: P lse rssul srinls hs ai sa ai ea i the w qt a 7 t9 h YI, .qta95 a l 21:11 whi h. s. $Q .P S iY and tha he t em t i l p v I v gthb'ftlie Pai pulse. The additional control pulses Pbf and P115 perniit totake care of this eventuality y I The P515 "and Pb' 'puls'es aregenerated by 'rno'nostable devices vvhichprq duce apulse starting at thesame time as the respective Pal aad'ra' pulses. This is indicated bysaus ss iiugl ,.Qta Paaru e results nih M p 1:, uiril ia ry "fol Pbfiaha R5 the links 6 and 7. Th'enatural period of these rnonostable re, pruc ed which pan lqe nsedas inputs for a threefdevices is designed to beequal to the normal duration 1 stabl ndition pulse cornp arator of thetype disclosed p fthe Pg and Pa pulses and the trailingcdges of the inthe 2} ye mentioned Belgian lja'tent No. 5 Q4,6Q. If positive Pb and Pbauxiliary control pulses are then t rlfa naalsat t a tnnla-ia a ssii enth. t i rwi re e tiv a se ta a m tt tra edge, rt e n a reductionfof the1e I gth of the conpylseto'istart the B17 1 control pulse and thetrailing edge alili n ile a will. he a steam n whi a 9 ..th.e. ?gm..pu$q dl trttlia bn bnt 's- ,fr 's e a 291. .will;ab i ins dw h a... 31.112ul w erein santrplt rwhfl hars wettes at n mm are indicated thepulse comparator Will react to indicate that the Ra the linksfi and}respectively joining'the links 2 and 3 PP39liQ?9F?i 9&gh-;.= in? Qtaahnd if the 25 Witne s an.add alsa wl t en P l for -Pa 's r t v ansaa a tasfliem the wtenXm i aPbu mp ai .rsQQ CBr' iL J its t l n edge w t ti'll also disappear and this ivilliiresult in the said produce thecontrol'pul se Pb butuill be prevented from pnlsecon'ip orreacting inthe sarne vvay to indicate the do 11g solas there is no coincidenttrailing edge of the a ea an 1t 3 117 1 415? a aaai 9a ?1'2,P r 'r' i qf E produci g theco trljpulses P1b andf the 1 ,11v Heiice; the latterpulse Will disappear devicesfor ,they rnay be nion'o stahle de- Ban icompar atoi'jwil l 'r eactinfthe right way indicating rfal periodfgreaterthan T In this last that thejfa' pnl se "granny. Additionally, theauxiliary P a for eigafnpleldisappears; the contrgl ulse stichas P5wilhalsopreveht the generation tv r i aq il s ar but h are sq tsl...i?i1,ai .isit f h P s l h f q jpnls eyvill also result in thel b con- Pais increased a b ove its normal value as in this case l inped fotaiduratiotl greater than also theltrailinq edger; eg lia pulse will comeafter errnrtung the pulse comparator to react in the the trailing edgeof the auxiliary control Pb pulse, vv ll v N h p notbe gatediby thelatter and generation ofthe control producing the c tro l pulses Pb ifinewinbejstegpea; :ihis has the advantage in lght ernonostalile dieviciesfo'f natural period 40 the l case-ofa p rsefce'mparat r reactingafter a delay t I T 'ifthecbntrol 'shovvn by the 11:11am and 5a'sjeigplainefdiabovei, that the pulse comparator will react ed. p I pia iaeaiateiywhea the P5 pulse exceeds a duration 1 hefaho'ye assumesthat if a lhereas vv 'thkjnitv the; auxiliary control pulses P11 and suea Pa i 'disappqarsi"it dies :away rapidly and P bigit'can oinlyreactripen the Pa and P11 pulses '1 "P pulseis norrn al.andlthere is'noreachi ,aj'len g'thj l t. the as act an p e .to il h f h hia 11 1 1 s jcillator' disappears, it does'so with h 'Pusv l v'l o ma Equal the s ltsi bn cbi l pul origin, displaced towards the left fwhrea the 2L 7 l;'pillsew 1d rern ain normal. This would c ause't lie comparator .toreact but to indicate the Pa pulse which lia's a n incorrect length.

, Q19 e v n a ra 1r si-" P551 control pulses will not lie generatedresume "'n" eactionofthe pulse c'omparator'indicating alfau lit infil ieprbperj half of the circuits concerned.

i th' ion ofthe comparator causes a f two p'ointsofitscircuit, 'ispsed'in conventionai nianner .7 W .s.l s. b ifisfal i= P s snate'usen'asap-arenas etert vi de ajbras f o r the "halfgofithe arrangenent which control grid of a gas tube with't p' mans cathode. p H Thi vblcching actron which L i i 111 Y- edby'bia f a h ndw entl o fthe lattercit ciiits of'appr opriat valves lieyond c uvoff, is electronic 1 i andtherefore practically instantaneous whereby within a titr ieles s' thanTtiie fatilty h'alf of the circuit is blocked.

Referring to Fig. 2, the latter illustratesaii'einbodirnent i "iihlockschirriati'c'fm m. It'r'e'pi'e'sents 'e 'tinie t h gr dpo alf'ofaip'ulse enter/patch is'prirnariiy" designed V i n atlv'an'c'e with tbsiipplytrigger ppisesfofperiod T 'which are used to'lse'distributorsofthering counter type,th'elatter the'cathiidepreveiitingthe"ionizationjof the'tube. Biit, g ri fp k r 'e t i a -beas" soon as the Pai pulse has" completely disappeared,'de'termmedphase' relationship'with respect to the others.

then the correspondingc'ontrol Pb 'pu'lsewill nolonger These pulseframes can. be used "to control switching devices of the static type(erg. using rectifiers) such as those aifording connections between acommon inlet and one out of a plurality of outlets on a time multiplexbasis.

Only half of the pulse generator is shown in Fig. 2 as the other half isexactly identical to the one shown and the vertical dash-dotted line onthe left-hand side of the figure is used to indicate that there existcircuits similar to those shown in Fig. 2 symmetrically arranged withrespect to the axial line.

The essential element for each half of a pulse generator is a pulseoscillator OSC which delivers positive pulses shown by Pa in Fig. 3. Tofix ideas, these pulses may be assumed to have a length of 25microseconds and to regularly recur with a period of 200 microseconds.Such a generator should be self-starting and extremely stable inoperation. One suitable for this purpose has been described in BelgianPatent 526,611 and consists of two valves with mutual anode-gridconnections and an LC anti-resonant circuit connected between the anodecircuits of the two valves and tuned to kc./s. The circuit is soarranged that the pulses can be delivered at the cathode of one of thevalves, i. e. at point P in Fig. 2.

These pulses are applied to the input of an amplifier AMP which need notbe further described as it may be of conventional design and comprisesfor example, a single triode, the plate of which is coupled to point PThe pulses appearing at P are therefore identical to those at point Pexcept that their polarity is reversed so that they consist in negativeinstead of positive pulses.

These pulses are fed to a phase splitter PHS which is also ofconventional design and it may, for example, consist of a single triodewith plate and cathode loads of substantially equal values. Assumingthat the plate of this last arrangement is connected to point P positivepulses will appear at this point and will be similar to those at P Thesepulses are fed to conductor L which leads to the other half of the pulsegenerating system (not shown). In particular, it leads to the identicalmaster pulse generator and corresponding with OSC so that the effect ofthe pulses at point P can be considered by assuming that thecorresponding pulses from the other half of the arrangement, i. e. frompoint P' (not shown), and present on conductor L are fed to OSC. Moreparticularly, if it is assumed that this generator OSC is of the typedisclosed in the above mentioned Belgian Patent 526,611, conductor L maybe connected to the grid of the triode at the cathode of which positivepulses are delivered (point P This connection will, of course, be madethrough a suitable coupling condenser (not shown), since the pulses atpoint P or point P' (not shown) are taken from the plate of a tube.

The positive pulses at point P go to a terminal Fu corresponding withthe pulse wave form shown in Fig. 3, through break contact b of relay BrThe cathode output of the phase splitter PHS is coupled to point P andthe pulses appearing thereat are of opposite polarity with respect tothose appearing at point P These negative pulses are applied to agenerator MMV which is a monostable multivibrator able to deliver anoutput pulse at terminal P in response to an input pulse at P Such amonostable pulse generator (nip-flop) may, for example, be obtained byusing two valves, the grid of the first being fed from point P the anodeof the first being capacitively coupled to the grid of the second, theanode of the latter being resistively coupled to the grid of the former,while the plate of the former is further coupled to point P Normally,the first valve with the grid fed from point P is in a nonconductivestate due to a more positive biassing for the second valve, whereby thenegative going leading edges of the pulses appearing at point P areinoperative to cause a change of conductivity for this tube, but thepositive going leading edges of the said negative pulses will cause 6 Vthe arrangement to trigger and the first valve is unblocked. The timeconstant of the monostable pulse generator MMV is so chosen that itdelivers pulses of t=25 micro-" seconds duration. These pulses, at pointP therefore follow immediately the pulses Pa The negative pulses atpoint P are fed to the input of a phase splitter PHS which is designedin exactly the same way as the phase splitter PHS Therefore, assumingthat point P is coupled to the plate of the valve forming the essentialpart of the phase splitter PHS positive pulses such as those shown inFig. 3 Will be obtained. These are the P6123 pulses, a corresponding P11terminal being shown connected to terminal P through break contact 11 ofrelay Br The pulses P6123 are further applied from terminal P to a pulseshaping circuit which produces at its output terminal P negative triggerpulses which are applied to terminal P6124 through break contact b ofrelay Br The corresponding Pa wave form is shown in Fig.- 3. The pulseshaping circuit PSI-I can comprise a monostable flip-flop circuit formedby two tubes coupled by their cathodes, the output tube including aninductance in its plate circuit designed to differentiate the front andrear flanks of the P6123 pulses. This valve arrangement is arranged todeliver only the trigger pulses corresponding to the leading edges ofthe Pa pulses and further includes an amplifying tube to the controlgrid to which these positive trigger pulses are applied, whereby thenegative trigger pulses shown as P11 in Fig. 3 are obtained at terminalP coupled to the anode of said amplifying tube. To fix ideas, thesepulses may be assumed to have a duration of some 4 microseconds.

These pulses are in a suitable form to be used as trigger pulses forpulse distributors in the manner disclosed in the Belgian Patent No.504,604. The reason for producing these trigger pulses from the positiverectangular Pa pulses and to produce also the rectangular positive P41pulses following immediately the Pa pulses, is that these last two typesof pulses can be conveniently used as stop and start pulses respectivelyfor the pulses of duration T equal to 200 microseconds which thedistributors (not shown) will deliver in response to the trigger pulsesPa The pulses delivered by the distributors can perform variousfunctions in telecommunication equipment and in the course of these,some may become distorted whereby it becomes necessary to regeneratethem and obtain fresh clean pulses. Such regeneration can convenientlyoccur with the help of a short pulse such as Pazg defining the start ofa distributor pulse and by means of a short pulse such as P41 definingthe end of a distributor pulse. The method of producing the triggerpulses P11 in conjunction with the short start and stop pulses Pa and P0is distinctive with respect to the method disclosed in the BelgianPatent No. 504,604 mentioned above, since in the latter trigger pulseswith a period t are first produced and these are applied to adistributor with a number of outlets which produces series of pulses allrecurring with a period T but shifted with respect to one another sothat one output from this distributor could be used to drive a pulseshaping circuit to obtain a series of pulses such as P11 with a period Twhereas two other outlets could be used to deliver the pulses Pam and PaSuch a distributor, however, necessitates a fairly large number ofvalves since at least two valves must be used for each outlet and sincethe number of outlets and tubes depends upon the ratio The Pa pulses arealso applied from terminal P to the input of a flip-flop or monostablemultivibrator cir cuit MMV which may correspond identically to the monostablesmultivibrator -MMV already described. At its Qutnutterminal Pthis flip-flop willdeliver pulses shown as'Pbss in .Fig. .3. Thesepulses are therefore identical to the B41 pulsesbut whereas the durationof the latter is fixed by the time constant of the flip-flop MMV theduration of the former is fixed by the time constant of the flip-flopMMV The Pb pulses at terminal P are fed to an integrating circuit lNTwhich can consist of a series resistor followed by a shunt condenser.

The second output from the phase splitter PHS delivered at terminal Pconsists in pulses similar to the P6123 pulses but with an invertedpolarity, since terminal P corresponds with the cathode of a tubewhereas terminal P corresponds with the plate of the same tube. Thenegative pulses at terminal P are applied to a difierentiating circuitDIF. which can consist of a series condenser followed; by a shuntresistor. The outputs of the integrating circuit INT and thediiterentiating circuit D1]? are commoned to terminal P which is theinput terminal of an amplifying circuit AMP which may be deemed similarto :the amplifying stage AMP This mixing of the two outputs will occurvia capacitive couplings including a condenserv in series with aresistor, i. e. a series combinationof a resistor and a condenser can beassumed to follow theshunt condenser in INT and a similar seriescombination can be assumed to follow the shunt resistor in DIE and berespectively included in said circuits INT and DIF. Both the seriesresistors should be designed sothat in relation to the input resistanceof the amplifier AMP they form suitable potentiometers for properlyadding the waveform from INT to that from DIF. The waveform from INT isshown as P11 and that from DIF asPb In the latter waveform, the negativespikes corresponding to the leading edges of the P11 pulses have notbeen...shown as they perform no useful function. The amplifierAMP isnormally biassed well below cut-ofii so that the P5 and P11 positivepulses cannot on their own unblockv the valve forming the amplifier AMPIt is only when a P12 positive pulse corresponds with the top part of aP11 pulse that the sum of these pulses willsufficiently raise thepotential at terminal P so that thevalve forming the amplifier AMP willbecome conductiveresulting in a negative pulse corresponding to theinverted top part of the P15 pulse appearing at its anode whichiscoupled to terminal P pulses which appear at terminal P uponcoincidence of a properly located Pb pulse with a properly located Pbgf,pulse are fed. to the input of a flip-flop or monostable multivibratorMMV which can be assumed to be designed in exactly the same way as theflip-flops MMV; t

and MMV but this time with a longer time constant, greater than T=200microseconds, e. g. 350 microseconds. Therefore, a negative triggerpulse at the terminal P11 Will result in the appearance of a positivepulse at P the output terminal from MMV Such pulses are shown as Pb inFig. 3.

Terminal P represents a second input for the flip-fiop MMV which is usedto restore the latter to its stable condition without. waiting for thenatural restoration which depends on the time constant of the circuit.To its terminaLP is connected the conductor L which originates intheother half of. the pulse generator and to which conductor L corresponds.Conductor L is therefore connected-to.aterminal- PC; (not shown) in theother half of thepulsegenerator, which terminal corresponds to terminal33 in that half of the geenrator shown in Fig. 2. This terminal is thesecond output from the phase splitter PHS and is coupled .to the cathodeof the tube forming this stage. Therefore, since terminal P is connectedto the anode of this same tube, the pulses at terminal P correspond withthe Pa pulses except that their polarity. isreversed. and that they aretherefore negative pulses: As terminal. P is coupled to the control gridof the valve part. of MMV which is normally conductive, terminal P willbe coupled to the other valve forming The negative trigger theteireuitMMv- 'gi. .e. that which is normallynon-tcom ductive but whichhas become conductive upon a negative trigger pulse having appeared :atterminal P as explained. Terminal P is .icoupled to the grid ofsaidother valve through a uni-directional capacitive coupling including acondenser in series with a rectifier, the latter being so poled thatonly the leading edges of the negative pulses at terminal P areefiective. Therefore, differentiated negative trigger pulsescorresponding in time with the leading edge of the P0 pulses areetfective to positively return the flip-flop MMV to its stable conditionwhen in the unstable condition. This results, during normal operation,in the positive pulses at terminal P assuming the shape shown as Pb inFig. 3. The pulses at terminal P are further delivered to a cathodefollower stage CPL which includes a tube having its cathode coupled tothe output terminal P Therefore, pulses similar to the Pb pulses willalso appear at terminal P The positive pulses at terminal P whichcorrespond to the control pulses Pb shown in Fig. l, are applied to aconductor L leading to the other half of the pulse generator. Thisconductor L has a counter part L connected to a terminal P (not shown)in the other half of the circuit and which acts as input conductor forthe gate G represented as a small circle with two conductors havingarrows pointing towards its centre. One of these is L and the other isthe conductor which carries the pulses delivered at terminal P A thirdconductor without an arrow is also shown pointing towards the centre ofthe small circle representing the gate G and it constitutes the outletconductor from this gate leading to the bistable electrical device A Thegate G is so arranged that a pulse .on conductor L will be allowed to bedelivered to the device A in its original or modified form if there isno coincident pulse on the conductor coming from terminal P A pulse onthis last conductor has thereby an inhibitive character which isindicated by a small line across the conductor next to the arrow.

The bistable device A is normally in one stable condition such that thepotential on its output conductor 1.; which is multipled to the circuitsOSC, MMV PSH and MMV does not exert any blocking action on thesecircuits which would prevent them to perform their normal tasks. As longas positive pulses are delivered at terminal P corresponding in thnewith pulses delivered at terminal P (not shown) and applied to conductorL13, the gate G does not issue an output pulse to the device A Upon apulse at terminal P being missed, the gate G will no longer be blockedand a pulse on conductor L will be allowed to trigger the device A intoits second stable condition in which the potential on conductor L issuificiently changed to block the circuits OSC, MMV PSH and MMV Thisaction is necessary, as the absence of a pulse at terminal P indicates afaulty condition in one of the circuits shown in Fig. 2 whereby thishalf of the pulse generator should instantaneously be disabled, theremaining half now supplying the full power to the common load. Theinstantaneous blocking action is also followed by a disconnection of theterminals P022, Pa and P1124 respectively from terminals P P and P asthe bistable device A which is being triggered to its second stable andoff normal condition also causes the operation of relay Br by applyingground (not shown) to the end of its winding which is not connected tonegative battery.

In -operating, relay B1? interrupts the circuits above men-.

tioned at contacts b 17 17 and locks through contact 12 and key contact1c, the later being used to restore relay Br to its tie-energizedcondition after the trouble has been cleared. It will be recognized thatthe arrangement G A Br represents one half of the pulse comparator, theremaining half not being shown as it is identical. to-that representedin Fig. 2. In practice, the gate function may be accomplished by thegrid cathode circuit of a gastube and the bistable device A maybeconstituted by the main gap of said gas tube associated with a relay, asdisclosed in the abovementioned Belgian Patent No. 504,605.

With the help of Fig. 3, the various faults which can occur and cause anappropriate reaction of the pulse comparator, can be readily followed.The essential difference with the basic diagram shown in Fig. 1 is thatthere are now two adjacent pulses such as Pa and Pa which are generatedinstead of a single pulse Pa as in Fig. 1. The control pulse Pb of Fig.3 corresponds to the control pulse Pb of Fig. 1 while the auxiliarycontrol pulse P11 of Fig. 3 corresponds with the auxiliary control pulsePb of Fig. 1.

If one of the devices PSI-I, MMV or INT develops a fault, the integratedgating pulse lb will not be generated and this will prevent thegeneration of the control pulse Pb at terminals P and P and as a resultthe bistable device A will be triggered to its olf normal conditionindicating the fault.

If there is a fault in MMV or PHS leading to the disappearance of the Papulse or to a change in length for said pulse, it is clear that thepulse comparator will again react in the same way.

If pulse P11 varies in length, this leads to pulse P11 being incorrectlylocated with respect to pulse Pb and again the control pulse Pb cannotbe generated.

If the devices MMV or CFL fail to deliver a control pulse, this againleads to the operation of A Concerning the auxiliary control pulsegenerator MMV it will be noticed that due to the integration of the Pbpulse being used to provide the gating pulse Pb only a reduction of thelength of the Pb pulse will prevent pulse Pb from causing a productionof the control pulse Pb If there is a lengthening of the P1723 pulse,the Pb pulse will still be allowed to trigger the flip-flop MMVresulting in the production of the control pulse Pb as if no fault hadbeen detected. This is of no consequence however, as the P12 pulseswhich have become too long, are not used in any external circuitry. Itonly means that if this fault in the auxiliary control pulse persistsuntil a fault is also originated in the generation of a PZ23 pulse,which might cause the latter pulse to increase its length unduly, thiswill not be detected until the length of the P323 pulse reaches twiceits normal length which corresponds to the delay in the response of thepulse comparator mentioned above in relation to Fig. 1.

The arrangement described and shown by Fig. 2 which constitutes a pilotgenerator for generating trigger pulses at a well defined frequency andwith full reliability of opeartion can be used in the system such asdescribed in the Belgian Patent No. 504,604 mentioned above. Preferably,however, it should be used as indicated in block schematic form in Fig.4.

This Fig. 4 represents two pilot generators PIL and PIL each of whichcorresponds to an arrangement shown in Fig. 2 and they are thereforemutually synchronized and provided with a control circuit as explainedabove. Normally, both the outlets of the pilot generators PIL; and PlLwill be commoned to all the inlets of the distributors which are drivenby the trigger pulses such as Pa and Pa A pair of distributors D18 andD18 is shown in Fig. 4 with the two inlets connected to the two outletsfrom PIL and PIL Both the devices such as PIL and D18 are normallydesigned so that they supply the right shape of wave form but powerstages are necessary to obtain the right amount of power required by theloads. A pair of outlets from corresponding stages in the pulsedistributors D18 and D18 are shown to be commoned to the inlets of threepower amplifiers POW FOW and POW which will supply in parallel thenecessary power for a common load. The normal connection of all theoutlets from one stage to all the inlets of the next stage for pulses ofthe same nature is advantageous in that instead of having twoindependent chains with several links, whereby one chain becomes uselessif one 10 link is broken resulting in complete failure should-:a link'in.theremaining chain be broken while the first broken-link has not beenrepaired, one has in fact a common chainand each link thereof is atleast duplicated whereby the. failure of one link can still be followedbefore it can bev corrected by the failure of other links notcorresponding with one another.

If for instance the pilot generator PIL the distributor D18 and thepower amplifier POW are defective, the load can still be supplied fromthe pilot generator PIL via the distributor D18 and the two poweramplifiers in parallel POW and POW which now deliver each one half ofthe total power instead of one third of the total power when all threepower amplifiers are in service.

While the principles of the invention have been described above inconnection with specific apparatus, it is to be clearly understood thatthis description is made only by way of example and not as a limitationon the scope of the invention.

We claim:

1. A control circuit for a pulse generating system having identicalfirst and second pulse oscillator continuously and normally producingcophasal output pulses of equal duration and period, means responsive tosaid output pulses from said first and second oscillators for producingfirst and second control pulses respectively, and means, controlled bythe control pulses and inoperative in the presence of both first andsecond control pulses, for blocking the oscillator whose correspondingcontrol pulse is absent during the presence of the control pulse of theother oscillator, characterized by means within said control pulseproducing means responsive to a change of duration of said output pulsesof said first and second oscillator in either direction as well as theirchange in phase or absence thereof for aborting the pulses of thecorresponding oscillator, said control pulse producing means comprisinga first and second two-output condition device each having a naturalperiod different from the normal repetition period of said oscillators,and means for applying said output pulses to said two-condition devices,the outputs of said two condition devices being coupled to the inputs ofsaid blocking means.

2. A control circuit according to claim 1 wherein said two-conditiondevices are monostable trigger devices whose natural period is greaterthan the normal repetition period of said oscillators.

3. A control circuit according to claim 1 wherein said devices comprisetrigger circuits and said means for applying thereto the output pulsesof said oscillator circuits includes means for applying the outputpulses of the first oscillator to the first trigger circuit to trip itfrom a first condition to a second and means for applying the outputpulses from the second oscillator to said first trigger circuit to tripit from its second to its first condition, and means for applying theoutput pulses of the second oscillator to the second trigger circuit totrip it from its first to its second condition and means for applyingthe output pulses from said first oscillator to said second triggercircuit to restore it to its first condition.

4. A control circuit according to claim 3 wherein said trigger circuitsare bi-stable trigger circuits.

5. A control circuit according to claim 3 further including for eachoscillator a third and a fourth monostable trigger circuit whose naturalperiods are such that their duration is equal to the normal duration ofthe output pulses of said oscillators, means for applying the outputpulses from each of said first and second oscillators to thecorresponding third and fourth trigger circuits and means for applyingthe output pulses from said third and fourth trigger circuits to saidfirst or second trigger circuit to initially trip it from its first toits second condition.

6. A control circuit according to claim 5 wherein said means forapplying the output pulses from said third trigger circuit to said firstor second trigger circuit comprises an integrating circuit, and whereinsaid means 12 Refrenc'sfitd in 'th' 'fi1eof- -thi fpatent UNITED STATESPATENTS 2,319,320 I-Iepp -May 18, 1943 2,330,582 Hepp Sept. 28, 19432,448,336 Weiner Aug. 31, 1948 2,538,027 Mozley et a1 Jan. 16, 1951

